Integrated Process For Producing Ethanol

ABSTRACT

In one embodiment, the invention is to a process for producing ethanol, the process comprising the steps of carbonylating methanol in a carbonylation system in the presence of a carbonylation catalyst under conditions effective to form acetic acid; hydrogenating the acetic acid in a hydrogenation system in the presence of a hydrogenation catalyst to form a crude ethanol product comprising ethanol and water; separating the ethanol from the water to form an ethanol stream and a water stream; and directing at least a portion of the water stream to the carbonylation system, e.g., for use as an extractant in a permanganate reducing compound removal system.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingethanol. In particular, the invention relates to processes for producingethanol from methanol via an acetic acid intermediate, in which waterformed in the ethanol synthesis step is recycled to the acetic acidsynthesis step.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal; from feed stockintermediates, such as syngas; or from starchy materials or cellulosematerials, such as corn and sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are often converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol. Inaddition, fermentation of starchy or cellulose materials competes withfood sources and places restraints on the amount of ethanol that can beproduced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. In the reduction of an alkanoicacid, such as acetic acid, water may be formed in an equal molar ratiowith ethanol. The need exists for uses for the excess water that isformed in the ethanol production process. The need also exists forintegrated processes for making ethanol from methanol.

SUMMARY OF THE INVENTION

The present invention is directed to integrated processes for formingethanol from methanol, preferably through an acetic acid intermediate.

In one embodiment, the invention is to a process for producing a waterstream. The process comprises the step of hydrogenating an acetic acidfeed stream to form a crude ethanol product. The crude ethanol productpreferably comprises ethanol, water, ethyl acetate, and acetic acid. Theprocess further comprises the step of separating at least a portion ofthe crude ethanol product in at least one column into a distillatecomprising ethanol and a residue comprising the water stream. The wateris directed to an acetic acid production process, preferably for use asan extractant for removing permanganate reducing compounds (PRC's) suchas acetaldehyde from a process stream contained in said acetic acidproduction process.

In another embodiment, the invention is to a process for carbonylatingmethanol in a carbonylation system in the presence of a carbonylationcatalyst under conditions effective to form acetic acid; hydrogenatingthe acetic acid in a hydrogenation system in the presence of ahydrogenation catalyst to form a crude ethanol product comprisingethanol and water; separating the ethanol from the water to form anethanol stream and a water stream; and directing at least a portion ofthe water stream to the carbonylation system.

In yet another embodiment, the invention is to a process for reactingcarbon monoxide with at least one reactant in a first reactor containinga reaction medium to produce a reaction solution comprising acetic acid,wherein the at least one reactant is selected from the group consistingof methanol, methyl acetate, methyl formate, dimethyl ether and mixturesthereof and wherein the reaction medium comprises water, acetic acid,methyl iodide, and a first catalyst; hydrogenating the acetic acid in ahydrogenation system in the presence of a hydrogenation catalyst to forma crude ethanol product comprising ethanol and water, separating theethanol from the water to form an ethanol stream and a water stream, anddirecting at least a portion of the water stream to the carbonylationsystem.

In yet another embodiment, the invention is to a process for producing awater stream, the process comprising providing a crude ethanol productcomprising ethanol, water, ethyl acetate, and acetic acid, separating atleast a portion of the crude ethanol product into an ethanol stream anda water stream, wherein the water stream is essentially free of organicimpurities other than acetic acid, and directing at least a portion ofthe water stream to a carbonylation system.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of an integrated system for formingethanol from methanol via an acetic acid intermediate in accordance withone embodiment of the present invention.

FIG. 2 is a schematic diagram of an acetic acid separation system, whichincludes a permanganate reducing compound removal system, in accordancewith one embodiment of the present invention.

FIG. 3 is a schematic diagram of a hydrogenation process having fourcolumns in accordance with an embodiment of the present invention.

FIG. 4 is a schematic diagram of another hydrogenation process havingtwo columns with an intervening water separation in accordance with anembodiment of the present invention.

FIG. 5 is a schematic diagram of another hydrogenation process havingtwo columns in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present invention relates to integrated processes for making ethanolfrom methanol. In one embodiment, the process includes a step ofcarbonylating methanol in a carbonylation system in the presence of acarbonylation catalyst under conditions effective to form acetic acid.The acetic acid is subsequently hydrogenated in a hydrogenation systemin the presence of a hydrogenation catalyst to form a crude ethanolproduct comprising ethanol and water. The crude ethanol product isseparated into an ethanol stream and a water stream. At least a portionof the water stream is then directed back to the carbonylation system.In a preferred embodiment, at least a portion of the water stream isused as an extractant in the carbonylation system, preferably as anextractant for removing permanganate reducing compounds (PRC's) such asacetaldehyde from one or more process streams in the carbonylationsystem.

FIG. 1 illustrates an integrated process 80 in accordance with oneembodiment of the present invention. Process 80 comprises carbonylationsystem 82 and hydrogenation system 84. Carbonylation system 82 receivesmethanol feed 86 and carbon monoxide feed 88. The methanol and thecarbon monoxide are reacted in carbonylation system 82 to form aceticacid. Carbonylation system 82, in some embodiments, further comprises apurification train comprising one or more distillation columns and/orextraction units (not shown in FIG. 1) to separate crude acetic acidinto an acetic acid product stream 90.

Acetic acid product stream 90 is fed, more preferably directly fed, tohydrogenation system 84. Hydrogenation system 84 also receives hydrogenfeed 92. In hydrogenation system 84, the acetic acid in acetic acidproduct stream 90 is hydrogenated to form a crude ethanol productcomprising ethanol and other compounds such as water, ethyl acetate, andunreacted acetic acid. Hydrogenation system 84 further comprises one ormore separation units, e.g., distillation columns and/or extractionunits (not shown in FIG. 1.), for separately recovering ethanol andwater from the crude ethanol product. An ethanol product stream 94 isthen recovered from hydrogenation system 84. As shown, water that isrecovered from the hydrogenation system is directed to the carbonylationsystem, as shown by water stream 96, where it may be used, for example,as an extraction agent for the removal of PRC's from one or more processstreams in carbonylation system 82. In a preferred embodiment, the waterstream 96 is used as an extraction unit for separating acetaldehyde fromone or more process streams in carbonylation system 82.

In addition to integrating the water stream between the hydrogenationsystem 84 and carbonylation system 82, the process may also beintegrated with methods for producing acetic acid and/or methods forproducing methanol. For example, acetic acid may be produced frommethanol, and thus ethanol production according to embodiments of thepresent invention may be produced from methanol. In one embodiment, thepresent invention comprises producing methanol from syngas,carbonylating the methanol to form acetic acid, and reducing acetic acidto form an alcohol, namely ethanol. In still another embodiment, thepresent invention comprises producing ethanol from a carbon source, suchas coal, biomass, petroleum, or natural gas, by converting the carbonsource to syngas, followed by converting the syngas to methanol,carbonylating the methanol to form acetic acid, and reducing acetic acidto form ethanol. In still another embodiment, the present inventioncomprises producing ethanol from a carbon source, such as coal, biomass,petroleum, or natural gas, by converting the carbon source to syngas,separating the syngas into a hydrogen stream and a carbon monoxidestream, carbonylating a methanol with the carbon monoxide stream to formacetic acid, and reducing acetic acid to form an ethanol. In addition,methanol may be produced from the syngas.

Various carbonylation systems and hydrogenation systems may be used inthe processes of the present invention. Exemplary materials, catalysts,reaction conditions, and separation processes that may be used in thecarbonylation and hydrogenation systems employed in the presentinvention are described further below.

Carbonylation System

In the carbonylation process, methanol is reacted with carbon monoxidein the presence of a carbonylation reactor under conditions effective toform acetic acid. In some embodiments, some or all of the raw materialsfor the carbonylation process may be derived partially or entirely fromsyngas. For example, the acetic acid may be formed from methanol andcarbon monoxide, both of which may be derived from syngas. The syngasmay be formed by partial oxidation reforming or steam reforming, and thecarbon monoxide may be separated from syngas. Similarly, hydrogen thatis used in the step of hydrogenating the acetic acid to form the crudeethanol mixture, as described in further detail below, may be separatedfrom syngas. The syngas, in turn, may be derived from variety of carbonsources. The carbon source, for example, may be selected from the groupconsisting of natural gas, oil, petroleum, coal, biomass, andcombinations thereof. Syngas or hydrogen may also be obtained frombio-derived methane gas, such as bio-derived methane gas produced bylandfills or agricultural waste.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with the hydrogenationsystem as noted above. U.S. Pat. No. 5,821,111, which discloses aprocess for converting waste biomass through gasification into synthesisgas, and U.S. Pat. No. 6,685,754, which discloses a method for theproduction of a hydrogen-containing gas composition, such as a synthesisgas including hydrogen and carbon monoxide, are incorporated herein byreference in their entireties.

The carbonylation of methanol, or another carbonylatable reactant,including, but not limited to, methyl acetate, methyl formate, dimethylether, or mixtures thereof, to acetic acid preferably occurs in thepresence of a Group VIII metal catalyst, such as rhodium, and ahalogen-containing catalyst promoter. A particularly useful process isthe low water rhodium-catalyzed carbonylation of methanol to acetic acidas exemplified in U.S. Pat. No. 5,001,259, the entirety of which isincorporated herein by reference.

Without being bound by theory, the rhodium component of the catalystsystem is believed to be present in the form of a coordination compoundof rhodium with a halogen component providing at least one of theligands of such coordination compound. In addition to the coordinationof rhodium and halogen, it is also believed that carbon monoxide willcoordinate with rhodium. The rhodium component of the catalyst systemmay be provided by introducing into the reaction zone rhodium in theform of rhodium metal, rhodium salts such as the oxides, acetates,iodides, carbonates, hydroxides, chlorides, etc., or other compoundsthat result in the formation of a coordination compound of rhodium inthe reaction environment.

The halogen-containing catalyst promoter of the catalyst systemcomprises a halogen compound, typically an organic halide. Thus, alkyl,aryl, and substituted alkyl or aryl halides can be used. Preferably, thehalogen-containing catalyst promoter is present in the form of an alkylhalide. Even more preferably, the halogen-containing catalyst promoteris present in the form of an alkyl halide in which the alkyl radicalcorresponds to the alkyl radical of the feed alcohol, which is beingcarbonylated. Thus, in the carbonylation of methanol to acetic acid, thehalide promoter will include methyl halide, and more preferably methyliodide.

The liquid reaction medium employed may include any solvent compatiblewith the catalyst system and may include pure alcohols, or mixtures ofthe alcohol feedstock and/or the desired carboxylic acid and/or estersof these two compounds. A preferred solvent and liquid reaction mediumfor the low water carbonylation process contains the desired carboxylicacid product. Thus, in the carbonylation of methanol to acetic acid, apreferred solvent system contains acetic acid.

Water is contained in the reaction medium but desirably atconcentrations well below that which has heretofore been thoughtpractical for achieving sufficient reaction rates. It has previouslybeen taught that in rhodium-catalyzed carbonylation reactions of thetype set forth in this invention, the addition of water exerts abeneficial effect upon the reaction rate. See, e.g., U.S. Pat. No.3,769,329, incorporated herein by reference in its entirety. Thus,commercial operations are commonly run at water concentrations of atleast about 14 wt. %. Accordingly, it has been quite unexpected thatreaction rates substantially equal to and above reaction rates obtainedwith such comparatively high levels of water concentration can beachieved with water concentrations below 14 wt. % and as low as about0.1 wt. %.

In accordance with the carbonylation process most useful to manufactureacetic acid according to the present invention, the desired reactionrates are obtained even at low water concentrations by maintaining inthe reaction medium an ester of the desired carboxylic acid and analcohol, desirably the alcohol used in the carbonylation, and anadditional iodide ion that is over and above the iodide ion that ispresent as hydrogen iodide. A desired ester is methyl acetate. Theadditional iodide ion is desirably an iodide salt, with lithium iodidebeing preferred. It has been found that under low water concentrations,methyl acetate and lithium iodide act as rate promoters only whenrelatively high concentrations of each of these components are presentand that the promotion is higher when both of these components arepresent simultaneously. See, e.g., U.S. Pat. No. 5,001,259, incorporatedherein by reference in its entirety. The concentration of iodide ionmaintained in the reaction medium of the preferred carbonylationreaction system is believed to be quite high as compared with whatlittle prior art there is dealing with the use of halide salts inreaction systems of this sort. The absolute concentration of iodide ioncontent is not a limitation on the usefulness of the present invention.

The carbonylation reaction of methanol to acetic acid product may becarried out by contacting the methanol feed with gaseous carbon monoxidebubbled through an acetic acid solvent reaction medium containing therhodium catalyst, methyl iodide promoter, methyl acetate, and additionalsoluble iodide salt, at conditions of temperature and pressure suitableto form the carbonylation product. It will be generally recognized thatit is the concentration of iodide ion in the catalyst system that isimportant and not the cation associated with the iodide, and that at agiven molar concentration of iodide the nature of the cation is not assignificant as the effect of the iodide concentration. Any metal iodidesalt, or any iodide salt of any organic cation, or quaternary cationsuch as a quaternary amine or phosphine or inorganic cation can bemaintained in the reaction medium provided that the salt is sufficientlysoluble in the reaction medium to provide the desired level of theiodide. When the iodide is a metal salt, preferably it is an iodide saltof a member of the group consisting of the metals of Group IA and GroupIIA of the periodic table as set forth in the “Handbook of Chemistry andPhysics” published by CRC Press, Cleveland, Ohio, 2002-03 (83rdedition). In particular, alkali metal iodides are useful, with lithiumiodide being particularly suitable. In the low water carbonylationprocess most useful in this invention, the additional iodide ion overand above the iodide ion present as hydrogen iodide is generally presentin the catalyst solution in amounts such that the total iodide ionconcentration is from about 2 to about 20 wt. % and the methyl acetateis generally present in amounts of from about 0.5 to about 30 wt. %, andthe methyl iodide is generally present in amounts of from about 5 toabout 20 wt. %. The rhodium catalyst is generally present in amounts offrom about 200 to about 2000 parts per million (ppm).

Typical reaction temperatures for carbonylation will be from 150 to 250°C., with the temperature range of 180 to 220° C. being a preferredrange. The carbon monoxide partial pressure in the reactor can varywidely but is typically about 2 to about 30 atmospheres, and preferably,about 3 to about 10 atmospheres. Because of the partial pressure ofby-products and the vapor pressure of the contained liquids, the totalreactor pressure will range from about 15 to about 40 atmospheres.

In the carbonylation of methanol, PRC's such as acetaldehyde and PRCprecursors may be formed as a byproduct, and as a result, thecarbonylation system preferably includes a PRC Removal System (PRS) forremoving such PRC's. PRC's may include, for example, compounds such asacetaldehyde, acetone, methyl ethyl ketone, butyraldehyde,crotonaldehyde, 2-ethyl crotonaldehyde, 2-ethyl butyraldehyde and thelike, and the aldol condensation products thereof. Thus, in someembodiments, the invention relates to processes for reducing and/orremoving PRC's or their precursors from intermediate streams during theformation of acetic acid by said carbonylation processes.

In particular, the present invention relates to a process in which acondensed light phase from a light ends column overhead is subjected toa distillation step to obtain an overhead that is subjected to a waterextraction step to selectively reduce and/or remove PRC's from theprocess. In one embodiment, the distillation step in the PRS includes asingle distillation column as described in U.S. Pat. No. 7,855,306, theentirety of which is incorporated herein by reference, while in otherembodiments the distillation step may include two or more distillationsteps as described, for example, in U.S. Pat. No. 6,143,930, theentirety of which is incorporated herein by reference. Similarly, in oneembodiment, the extraction step in the PRS includes a single extractionunit, while in other embodiments, multiple extraction units employingthe same or different extractants, may be employed, as described forexample, in U.S. Pat. No. 7,223,886, the entirety of which isincorporated herein by reference. Although the PRS is illustrated anddescribed herein as having a single distillation column and a singleextraction unit, it should be understood that the principles of theinvention may be employed with separation systems having multipledistillation columns and/or multiple extraction units.

A typical reaction and acetic acid recovery system that is used for theiodide-promoted rhodium catalyzed carbonylation of methanol to aceticacid is shown in FIG. 2 and includes a liquid phase carbonylationreactor, flasher, and a light ends column 14. In the process,carbonylation product obtained in the reactor (not shown) is provided tothe flasher (not shown) where a volatile (“vapor”) overhead stream 26comprising acetic acid and a less volatile catalyst phase (not shown),comprising a catalyst-containing solution are obtained. The volatileoverhead stream 26 comprising acetic acid is provided to the light endscolumn 14 where distillation yields a purified acetic acid product thatis removed via sidestream 17 and an overhead distillate stream 28(hereafter “low-boiling overhead vapor stream”). Acetic acid removed viasidestream 17 can be subjected to further purification, such as to adrying column (not shown) for selective separation of acetic acid fromwater. In a preferred embodiment, acetic acid derived from sidestream17, optionally after processing in one or more additional separationunits, e.g., drying column and/or resin guard beds, is directed to thehydrogenation system, described below, where it is reduced with hydrogenin the presence of a hydrogenation catalyst under conditions effectiveto form ethanol.

As they constitute standard equipment, well known in the art, thereactor and flasher are not shown in FIG. 2. The carbonylation reactoris typically either a stirred vessel or bubble-column type within whichthe reacting liquid or slurry contents are maintained automatically at aconstant level. Into this reactor, fresh methanol, carbon monoxide andsufficient water as needed to maintain at least a finite concentrationof water in the reaction medium are continuously introduced. Alsointroduced into the reactor is a recycled catalyst solution, such asfrom the flasher base, a recycled methyl iodide phase, a recycled methylacetate phase, and a recycled aqueous acetic acid phase. A recycledphase may contain one or more of the foregoing components.

Distillation systems are employed that provide means for recovering thecrude acetic acid and recycling catalyst solution, methyl iodide, methylacetate, and other system components within the process. In a typicalcarbonylation process, carbon monoxide is continuously introduced intothe carbonylation reactor, desirably below the agitator, which is usedto stir the contents. The gaseous feed is thoroughly dispersed throughthe reacting liquid by this stirring means. A gaseous purge stream isdesirably vented from the reactor to prevent buildup of gaseousby-products and to maintain a set carbon monoxide partial pressure at agiven total reactor pressure. The temperature of the reactor iscontrolled and the carbon monoxide feed is introduced at a ratesufficient to maintain the desired total reactor pressure.

Liquid product is drawn off from the carbonylation reactor at a ratesufficient to maintain a constant level therein and is introduced to theflasher. In the flasher, a catalyst-containing solution (catalyst phase)is withdrawn as a base stream (predominantly acetic acid containing therhodium and the iodide salt along with lesser quantities of methylacetate, methyl iodide, and water), while a vapor overhead streamcomprising acetic acid is withdrawn overhead. The vapor overhead streamcomprising acetic acid also contains methyl iodide, methyl acetate, andwater. Dissolved gases exiting the reactor and entering the flashercomprise a portion of the carbon monoxide and may also contain gaseousby-products such as methane, hydrogen, and carbon dioxide. Suchdissolved gases exit the flasher as part of the overhead stream. Theoverhead stream is directed to the light ends column 14 as stream 26.

It has been disclosed in U.S. Pat. Nos. 6,143,930 and 6,339,171 thatthere is generally a higher concentration of the PRC's and in particularacetaldehyde content in the low-boiling overhead vapor stream 28 exitingcolumn 14 than in the high-boiling residue stream exiting column 14.Thus, in accordance with the present invention, low-boiling overheadvapor stream 28 containing PRC's is subjected to additional processingto reduce and/or remove the amount of PRC's present. Low-boilingoverhead vapor stream 28, therefore, is condensed and directed to anoverhead receiver decanter 16. In addition to PRC's, low-boilingoverhead vapor stream 28 will typically contain methyl iodide, methylacetate, acetic acid, and water. Conditions are desirably maintained inthe process such that low-boiling overhead vapor stream 28, once indecanter 16, will separate into a light phase and a heavy phase.Generally, low-boiling overhead vapor stream 28 is chilled to atemperature sufficient to condense and separate the condensable methyliodide, methyl acetate, acetaldehyde and other carbonyl components, andwater into two phases. A portion of stream 28 may include noncondensablegases such as carbon dioxide, hydrogen, and the like that can be ventedas shown in stream 29 on FIG. 2.

The condensed light phase in decanter 16 will generally comprise water,acetic acid, and PRC's, as well as quantities of methyl iodide,methanol, and methyl acetate. The condensed heavy phase in decanter 16will generally comprise methyl iodide, methyl acetate, and methanol.While either phase of the light ends overhead, i.e., low-boilingoverhead vapor stream 28, may be subsequently processed to remove thePRC's and primarily the acetaldehyde component of the stream, the PRC'sare preferably removed from the condensed light phase 30. Thus, thecondensed heavy phase in the decanter 16 can be convenientlyrecirculated, either directly or indirectly, to the reactor (not shownin FIG. 2), and optionally recirculated with a portion of the lightphase. For example, a portion of this condensed heavy phase can berecirculated to the reactor, with a slip stream, generally a smallamount, e.g., 25 vol. %, preferably less than about 20 vol. %, of theheavy phase being directed to a carbonyl treatment process. This slipstream of the heavy phase may be treated individually or may be combinedwith the condensed light phase 30 for further distillation andextraction of carbonyl impurities.

In a preferred embodiment, the overall carbonylation process includes astep of distilling PRC's, primarily aldehydes such as acetaldehyde, froma low-boiling overhead vapor stream, particularly the condensed lightphase of a low-boiling overhead vapor stream 28 from a light endsdistillation column 14. In accordance with the present invention, acondensed light phase of a low-boiling overhead vapor stream 28 from alight ends distillation column 14 is distilled in one or moredistillation columns and then subjected to single- or multi-stageextraction to reduce and/or remove PRC's. Preferably water derived fromthe hydrogenation system, described below, is employed as an extractionagent in at least one of the extraction stages.

Condensed light phase 30 is directed to one or more distillation columns18 (one is shown), which serve to form a second vapor phase 36 enrichedin PRC's, notably acetaldehyde, but also containing methyl iodide due tothe similar boiling points of methyl iodide and acetaldehyde. Secondvapor phase 36 is condensed and then extracted with water to reduceand/or remove PRC's, notably acetaldehyde. In a preferred embodiment aportion of the condensed stream 36 is provided as reflux to distillationcolumn 18. This can be accomplished, as shown in FIG. 2, by provided thecondensed stream 36 to an overhead receiver 20, from which a portion ofcondensed stream 36 can be provided to the extraction step (generallyindicated as 70) by stream 40 and another portion of condensed stream 36can be provided as reflux to distillation column 18 by stream 42.

Acetaldehyde is extracted by water to obtain an aqueous acetaldehydestream 72, which may be treated as waste. The raffinate from theextraction, notably containing methyl iodide is desirably returned tothe carbonylation process, e.g., to the reactor, the light ends columnor the decanter 16, by stream 74. Aqueous acetaldehyde stream 72optionally is stripped of aldehyde for treatment as waste with waterbeing recirculated for use in the process.

A primary concern is in the extraction step that separates acetaldehydefrom methyl iodide. The efficiency of this separation is primarilyaffected by the relative solubility of acetaldehyde and methyl iodide inwater. While acetaldehyde is miscible in water, methyl iodide is not.However, the solubility of methyl iodide in water increases, with aconcomitant loss of methyl iodide from the process system, withincreasing levels of methyl acetate and/or methanol. At high enoughmethyl acetate and/or methanol levels, phase separation of methyl iodidein the water extraction may not occur. Similarly, phase separation ofmethyl iodide in the water extraction may not occur if acetic acidconcentrations are sufficiently high. Thus, it is desirable that thedistillate that is condensed and provided for extraction containmethanol and methyl acetate at a combined concentration of less thanabout 10 wt %, more desirably less than about 5 wt. %, even moredesirably less than about 2 wt. %, and even more desirably less thanabout 1.5 wt. %. It is desirable that the distillate that is condensedand provided for extraction contains less than about 3 wt. % aceticacid, more desirably less than about 1 wt. %, and even more desirablyless than about 0.5 wt. %. Particularly desired would be acetic acidconcentrations approaching zero wt. %. The water purge streams from thehydrogenation process are well suited to be used as an extractant due tothe relatively low concentrations of methyl acetate and/or methanol, aswell as acetic acid.

Thus, in the process of the present invention, a single distillation isconducted in distillation column 18 under conditions designed tocontrol, notably minimize, the quantities of methyl acetate and aceticacid in second vapor phase stream 36. Desirably, minimization ofquantities of methyl acetate and acetic acid in second vapor phasestream 36 is achieved while simultaneously maintaining higheracetaldehyde levels in second vapor phase stream 36 than in the residuumof distillation column 18. It is desirable that the residuum ofdistillation column 18 contain less than about 0.3 wt. % acetaldehyde,more desirably less than about 0.2 wt. %, and even more desirably lessthan about 0.1 wt. %. Particularly desired would be acetaldehydeconcentrations approaching zero wt. %.

Thus, in accordance with one embodiment of the present invention,illustrated in FIG. 2, low-boiling overhead vapor stream 28 is condensedin overhead receiver decanter 16 where it is biphasically separated toform a condensed heavy phase and a light condensed liquid phase 30. Thelight condensed liquid phase 30 is provided to distillation column 18via stream 30/32. In this and other embodiments of the presentinvention, a portion of stream 30 can be directed back to the light endscolumn 14 as reflux stream 34.

In distillation column 18, a second vapor phase stream 36 overhead and ahigher boiling liquid phase residuum stream 38 are formed. The secondvapor phase stream 36 overhead is enriched with PRC's, notablyacetaldehyde, with respect to the light condensed liquid phase 30. Thesecond vapor phase stream 36 overhead is deficient with methyl acetate,methanol, and/or acetic acid (desirably all three) with respect to saidlight condensed liquid phase 30. The higher boiling liquid phaseresiduum stream 38 is enriched with methyl acetate, methanol, and/oracetic acid (desirably all three) with respect to said second vaporphase stream 36. Desirably, the second vapor phase stream 36 overhead isenriched with PRC's, notably acetaldehyde, with respect to the higherboiling liquid phase residuum stream 38. The higher boiling liquid phaseresiduum stream 38 can be, and preferably is, retained in the process.

One of ordinary skill in the art having the benefit of this disclosurecan design and operate a distillation column to achieve the desiredresults of the present invention. Such efforts, although possiblytime-consuming and complex, would nevertheless be routine for one ofordinary skill in the art having the benefit of this disclosure.Accordingly, the practice of this invention is not necessarily limitedto specific characteristic of a particular distillation column or theoperation characteristics thereof, such as the total number of stages,the feed point, reflux ratio, feed temperature, reflux temperature,column temperature profile, and the like.

Further in accordance with this first embodiment of the presentinvention, second vapor phase stream 36 is extracted with water(generally indicated by 70), which is derived at least in part from thewater stream formed in the hydrogenation system, as described below, toremove and/or reduce PRC's, notably acetaldehyde. Acetaldehyde isextracted by the water to obtain aqueous acetaldehyde stream 72, whichis PRC-rich, and in particular acetaldehyde-rich. Aqueous acetaldehydestream 72 will generally be treated as a waste, although in someembodiments acetaldehyde may be stripped, with the water optionallybeing recirculated to the process. The raffinate, notably containingmethyl iodide is desirably returned to the carbonylation process bystream 74. The efficiency of the extraction will depend on such thingsas the number of extraction stages and the water to feed ratio.

Extraction with water 70 can be either a single stage or multistageextraction and any equipment used to conduct such extractions can beused in the practice of the present invention. Multistage extraction ispreferred. For example, extraction 70 can be accomplished by combiningstream 40 with water derived at least in part from the hydrogenationsystem and providing the combination successively to a mixer and then aseparator. Multiple mixer/separator combinations can be operated inseries to obtain a multistage extraction. Optionally, and desirably,multistage extraction is accomplished in a single vessel having a seriesof trays. The vessel may be equipped with paddle(s) or other mechanismsfor agitation to increase extraction efficiency. In such a multistageextraction vessel, stream 40 is desirably provided proximate to one endof the vessel with water being provided proximate to the other end ofthe vessel or such other location to obtain a countercurrent flow.

The mutual solubility between the two phases in the extraction canincrease with temperature. Accordingly, it is desirable that theextraction be conducted at a combination of temperature and pressuresuch that the extractor contents can be maintained in the liquid state.Moreover, it is desirable to minimize the temperatures to which stream40 is exposed to minimize the likelihood of polymerization andcondensation reactions involving acetaldehyde. Although it is preferredto use water from the hydrogenation system, water used in the extraction70 may also be taken from an internal carbonylation stream so as tomaintain water balance within the carbonylation system. Dimethyl ether(DME) may also be introduced to the extraction to improve the separationof methyl iodide in the extraction, i.e., to reduce the loss of methyliodide into the aqueous acetaldehyde stream 72. The DME can beintroduced to the process or formed in situ.

In accordance with another embodiment, also illustrated in FIG. 2,low-boiling overhead vapor stream 28 is condensed in decanter 16 whereit is biphasically separated to form a condensed heavy phase and acondensed light phase 30. The condensed light phase 30 is provided todistillation column 18 via stream 30/32. Again, in this and otherembodiments of the present invention, a portion of stream 30 can bedirected back to the light ends column 14 as reflux stream 34. Indistillation column 18, a second vapor phase stream 36 overhead and ahigher boiling liquid phase residuum stream 38 are formed. A sidestream80, comprising methyl acetate, is also taken. Thus, sidestream 80 may ormay not be included in the PRS system.

If used, sidestream 80 allows the distillation column 18 to be operatedunder conditions desirable for obtaining a higher concentration ofacetaldehyde in second vapor phase stream 36 while providing a mechanismfor removing methyl acetate that might otherwise build up in the centerof distillation column 18 or be pushed into the second vapor phasestream 36 overhead. The sidestream 80, comprising methyl acetate, ispreferably retained in the process.

In embodiments employing sidestream 80, the second vapor phase stream 36overhead is enriched with PRC, notably acetaldehyde, with respect tolight condensed liquid phase 30. The second vapor phase stream 36overhead is deficient with methyl acetate, methanol, and/or acetic acid(desirably all three) with respect to light condensed liquid phase 30.The second vapor phase stream 36 overhead is deficient with methylacetate, methanol, and/or acetic acid (desirably all three) with respectto said sidestream 80 and, desirably, also with respect to the higherboiling liquid phase residuum stream 38. Desirably, the second vaporphase stream 36 overhead is enriched with PRC's, notably acetaldehyde,with respect to both the sidestream 80 and the higher boiling liquidphase residuum stream 38.

Further in accordance with this second embodiment of the presentinvention, second vapor phase stream 36 is extracted with water(generally indicated by 70) derived at least in part from the waterstream formed in the hydrogenation system, as described below, to removeresidual PRC's, notably acetaldehyde. When water is used as anextractant, it may be preferable to use a portion of the water ofreaction in the hydrogenation process. Extraction in accordance withthis second embodiment is conducted in accordance with the extractionprocedures disclosed for the first embodiment.

Operating without a sidestream 80, the process has been found to achievethe following results respecting the separation capabilities ofdistillation column 18, as shown in Table 1.

TABLE 1 EXEMPLARY STREAM COMPOSITIONS WITHOUT SIDESTREAM 80 WeightPercent Weight Percent Weight Percent Component in Stream 30/32 inStream 36 in Stream 38 Methyl iodide 1.5 74.5 <0.1 Methyl acetate 6.01.4 6.1 Methanol 4.0 0.2 4.1 Acetic acid 15 <0.1 15.3 Water 73 1.6 74.5Acetaldehyde 0.5 22.2 0.1

Operating with a sidestream 80, it is expected that the followingresults respecting the separation capabilities of distillation column 18can be achieved, as shown in Table 2.

TABLE 2 EXEMPLARY STREAM COMPOSITIONS WITH SIDESTREAM 80 Weight WeightWeight Weight Percent in Percent in Percent in Percent in ComponentStream 30/32 Stream 36 Stream 38 Stream 80 Methyl iodide 1.5 46.8 <0.128.7 Methyl acetate 4.0 0.4 1.7 60.4 Methanol 1.0 <0.1 1.0 0.5 Aceticacid 15 <0.1 15.7 0.5 Water 78 0.8 81.6 7.4 Acetaldehyde 0.5 52 <0.1 2.5

This process has been found to reduce and/or remove PRC's and theirprecursors, multi-carbon alkyl iodide impurities, and propionic andhigher carboxylic acids from the carbonylation process. It has also beenshown that acetaldehyde and its derivatives are reduced and/or removedby sufficient amounts such that it is possible to keep the concentrationof propionic acid in the acetic acid product below about 500 parts permillion by weight, preferably below about 300 parts per million, andmost preferably below 250 parts per million.

In variations of the embodiments of the present invention, it isimportant to inhibit the formation of various aldehyde related polymersand condensation products in distillation column 18. Acetaldehydepolymerizes to form metaldehyde and paraldehyde. These polymersgenerally are low molecular weight, less than about 200. Highermolecular weight polymers of acetaldehyde can also form. These highermolecular weight polymers (molecular weight greater than about 1000) arebelieved to form during processing of the light phase and are viscousand thixotropic. Acetaldehyde can also undergo undesirable aldolcondensation reactions.

The formation of these impurities, i.e., metaldehyde and paraldehyde andhigher molecular weight polymers of acetaldehyde, can be suppressed byintroducing into distillation column 18 a flush stream containing atleast water and/or acetic acid.

Hydrogenation System

As discussed above, the processes of the invention integrate acarbonylation system with a hydrogenation system. The hydrogenationsystem preferably includes a hydrogenation reactor and a hydrogenationcatalyst system effective in converting acetic acid to ethanol andwater. The hydrogenation system also includes a separation system forseparating a crude ethanol product into an ethanol product stream, awater stream (which is directed at least in part to the carbonylationsystem, e.g., an extraction unit in said carbonylation system), andoptionally one or more byproduct streams.

In addition to acetic acid, the acetic acid feed stream that is fed tothe hydrogenation reactor may comprise other carboxylic acids andanhydrides, as well as aldehydes and/or ketones, such as acetaldehydeand acetone. Preferably, a suitable acetic acid feed stream comprisesone or more compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These compounds may also be hydrogenated in the processes of the presentinvention. In some embodiments, the presence of some carboxylic acids,such as propanoic acid or its anhydride, may be beneficial in producingpropanol. Water may also be present in the acetic acid feed.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

The reactor, in some embodiments, may include a variety ofconfigurations using a fixed bed reactor or a fluidized bed reactor. Inmany embodiments of the present invention, an “adiabatic” reactor can beused; that is, there is little or no need for internal plumbing throughthe reaction zone to add or remove heat. In other embodiments, a radialflow reactor or reactors may be employed as the reactor, or a series ofreactors may be employed with or without heat exchange, quenching, orintroduction of additional feed material. Alternatively, a shell andtube reactor provided with a heat transfer medium may be used. In manycases, the reaction zone may be housed in a single vessel or in a seriesof vessels with heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation in the reactor may be carried out in either the liquidphase or vapor phase. Preferably, the reaction is carried out in thevapor phase under the following conditions. The reaction temperature mayrange from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225°C. to 300° C., or from 250° C. to 300° C. The pressure may range from 10kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500kPa. The reactants may be fed to the reactor at a gas hourly spacevelocity (GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹,greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms ofranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst in the reactor. Suitablehydrogenation catalysts include catalysts comprising a first metal andoptionally one or more of a second metal, a third metal or any number ofadditional metals, optionally on a catalyst support. The first andoptional second and third metals may be selected from Group IB, IIB,IIIB, IVB, VB, VIIB, VIIB, VIII transition metals, a lanthanide metal,an actinide metal or a metal selected from any of Groups IIIA, IVA, VA,and VIA. Preferred metal combinations for some exemplary catalystcompositions include platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S. Pub.No. 2010/0029995, the entireties of which are incorporated herein byreference. In another embodiment, the catalyst comprises a Co/Mo/Scatalyst of the type described in U.S. Pub. No. 2009/0069609, theentirety of which is incorporated herein by reference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include those selected from thegroup consisting of WO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO, Co₂O₃, andBi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint-Gobain N or Pro. The Saint-Gobain Nor Pro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol in the reactor. For purposes of the present invention, the term“conversion” refers to the amount of acetic acid in the feed that isconverted to a compound other than acetic acid. Conversion is expressedas a mole percentage based on acetic acid in the feed. For example,acetic acid may have a conversion that is greater than 40%, e.g.,greater than 50%, greater than 70% or greater than 90%. The conversionmay vary and may be from 40% to 70% in some embodiments and from 85% to99% in others.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, in the reactor, theselectivity to ethanol is at least 80%, e.g., at least 85% or at least88%. Preferred embodiments of the hydrogenation process also have lowselectivity to undesirable products, such as methane, ethane, and carbondioxide. The selectivity to these undesirable products preferably isless than 4%, e.g., less than 2% or less than 1%. More preferably, theseundesirable products are present in undetectable amounts. Formation ofalkanes may be low, and ideally less than 2%, less than 1%, or less than0.5% of the acetic acid passed over the catalyst is converted toalkanes, which have little value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolmixture produced by the reactor, before any subsequent processing, suchas purification and separation, will typically comprise acetic acid,ethanol and water. Exemplary compositional ranges for the crude ethanolmixture are provided in Table 3. The “others” identified in Table 3 mayinclude, for example, esters, ethers, aldehydes, ketones, alkanes, andcarbon dioxide.

TABLE 3 CRUDE ETHANOL MIXTURE COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70 15 to50 25 to 50 Acetic Acid 0 to 90  0 to 50  5 to 70  5 to 50 Water 5 to 35 5 to 28 10 to 26 10 to 22 Ethyl Acetate 0 to 30  0 to 20  1 to 12  3 to10 Acetaldehyde 0 to 10 0 to 3 0.1 to 3   0.2 to 2   Diethyl Acetal0.001 to 5    0.01 to 3   0.1 to 2   0.5 to 1.5 Others 0.1 to 10   0.1to 6   0.1 to 4   —

In one embodiment, the crude ethanol mixture may comprise acetic acid inan amount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt.% or less than 5 wt. %. In embodiments having lower amounts of aceticacid, the conversion of acetic acid is preferably greater than 75%,e.g., greater than 85% or greater than 90%. In addition, the selectivityto ethanol may also be preferably high, and is greater than 75%, e.g.,greater than 85% or greater than 90%.

Ethanol may be recovered using several different techniques. In FIG. 3,hydrogenation section separates the crude ethanol mixture using threecolumns 120, 123, 128 and/or an optional fourth column 131. In FIG. 4,the crude ethanol mixture is separated in two columns with anintervening water separation step. In FIG. 5, the separation of thecrude ethanol mixture uses two columns. Other separation systems mayalso be used with embodiments of the present invention. For purposes ofconvenience, the columns in each exemplary separation process may bereferred to as the first column, second column, third column, etc., butit should be understood that similarly named columns of the embodimentsshown in FIGS. 3-5 will operate differently from one another.

In each of the figures, hydrogenation system 100 includes a reactionzone 101 and a separation zone 102. Hydrogen and acetic acid are fed vialines 104 and 105, respectively, to a vaporizer 106 to create a vaporfeed stream in line 107 that is directed to reactor 103. In oneembodiment, lines 104 and 105 may be combined and jointly fed tovaporizer 106. The temperature of the vapor feed stream in line 107 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 106 and may be recycled thereto or discarded. In addition,although line 107 is shown as being directed to the top of reactor 103,line 107 may be directed to the side, upper portion, or bottom ofreactor 103.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 106, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol mixture stream is withdrawn, preferablycontinuously, from reactor 103 via line 109.

The crude ethanol mixture stream in line 109 may be condensed and fed toa separator 110, which, in turn, provides a vapor stream 111 and aliquid stream 112. In some embodiments, separator 110 may comprise aflasher or a knockout pot. The separator 110 may operate at atemperature of from 20° C. to 250° C., e.g., from 30° C. to 225° C. orfrom 60° C. to 200° C. The pressure of separator 110 may be from 50 kPato 2000 kPa, e.g., from 75 kPa to 1500 kPa or from 100 kPa to 1000 kPa.Optionally, the crude ethanol mixture in line 109 may pass through oneor more membranes to separate hydrogen and/or other non-condensablegases.

The vapor stream 111 exiting separator 110 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101.When returned to reaction zone 101, vapor stream 110 may be combinedwith the hydrogen feed 104 and co-fed to vaporizer 106. In someembodiments, the returned vapor stream 111 may be compressed beforebeing combined with hydrogen feed 104.

In FIG. 3, the liquid stream 112 from separator 110 is withdrawn andpumped to the side of first column 120, also referred to as an “acidseparation column.” In one embodiment, the contents of liquid stream 112are substantially similar to the crude ethanol mixture obtained from thereactor, except that the composition has been depleted of hydrogen,carbon dioxide, methane and/or ethane, which are removed by separator110. Accordingly, liquid stream 112 may also be referred to as a crudeethanol mixture. Exemplary components of liquid stream 112 are providedin Table 4. It should be understood that liquid stream 112 may containother components, not listed in Table 4.

TABLE 4 COLUMN FEED COMPOSITION (Liquid Stream 112) Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 5 to 70 10 to 60 15 to 50 Acetic Acid <90 5 to 80  5 to 70 Water 5 to 35  5 to 28 10 to 26 Ethyl Acetate <300.001 to 20    1 to 12 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal<5  0.001 to 2    0.005 to 1    Acetone <5  0.0005 to 0.05  0.001 to0.03  Other Esters <5  <0.005 <0.001 Other Ethers <5  <0.005 <0.001Other Alcohols <5  <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout presentspecification are preferably not present and if present may be presentin trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 4 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 4 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 4 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the liquid stream 112may comprise propanol, e.g., isopropanol and/or n-propanol, in an amountfrom 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03wt. %. In should be understood that these other components may becarried through in any of the distillate or residue streams describedherein and will not be further described herein, unless indicatedotherwise.

Optionally, crude ethanol mixture in line 109 or in liquid stream 112may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeresidual acetic acid present in the crude ethanol mixture to furtherreduce the amount of acetic acid that would otherwise need to beremoved. Hydrogenolysis may be used to convert ethyl acetate in thecrude ethanol mixture to ethanol.

In the embodiment shown in FIG. 3, line 112 is introduced in the lowerpart of first column 120, e.g., lower half or lower third. In firstcolumn 120, acetic acid, a portion of the water, and other heavycomponents, if present, are removed from the composition in line 121 andare withdrawn, preferably continuously, as residue. Some or all of theresidue may be returned and/or recycled back to reaction zone 101 vialine 121. Recycling the acetic acid in line 121 to the vaporizer 106 mayreduce the amount of heavies that need to be purged from vaporizer 106.Reducing the amount of heavies to be purged may improve efficiencies ofthe process while reducing byproducts.

First column 120 also forms an overhead distillate, which is withdrawnin line 122, and which may be condensed and refluxed, for example, at aratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.The distillate in line 122 comprises primarily ethanol, as well aswater, ethyl acetate, acetaldehyde, and/or diethyl acetal. For example,distillate may comprise from 20 to 75 wt. % ethanol and 10 to 40 wt. %ethanol. Preferably, the concentration of acetic acid in the distillateis less than 2 wt. %, e.g., less than 1 wt. % or less than 0.5 wt. %.

In one embodiment, first column 120 may be operated at ambient pressure.In other embodiments, the pressure of first column 120 may range from0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375kPa. When first column 120 is operated under standard atmosphericpressure, the temperature of the residue exiting in line 121 preferablyis from 95° C. to 120° C., e.g., from 110° C. to 117° C. or from 111° C.to 115° C. The temperature of the distillate exiting in line 122preferably is from 70° C. to 110° C., e.g., from 75° C. to 95° C. orfrom 80° C. to 90° C.

As shown, the first distillate in line 122 is introduced to the secondcolumn 123, also referred to as the “light ends column,” preferably inthe middle part of column 123. Preferably the second column 123 is anextractive distillation column, and an extraction agent is added theretovia lines 124 and/or 125. Extractive distillation is a method ofseparating close boiling components, such as azeotropes, by distillingthe feed in the presence of an extraction agent. The extraction agentpreferably has a boiling point that is higher than the compounds beingseparated in the feed. In preferred embodiments, the extraction agent iscomprised primarily of water. As indicated above, the first distillatein line 122 that is fed to the second column 123 comprises ethanol,water, and ethyl acetate. These compounds tend to form binary andternary azeotropes, which decrease separation efficiency. As shown, inone embodiment the extraction agent comprises the third residue in line124. Preferably, the recycled third residue in line 124 is fed to secondcolumn 123 at a point higher than the first distillate in line 122. Inone embodiment, the recycled third residue in line 124 is fed near thetop of second column 123 or fed, for example, above the feed in line 122and below the reflux line from the condensed overheads. In a traycolumn, the third residue in line 124 is continuously added near the topof the second column 123 so that an appreciable amount of the thirdresidue is present in the liquid phase on all of the trays below. Inanother embodiment, the extraction agent is fed from a source outside ofthe process 100 via line 125 to second column 123. Preferably thisextraction agent comprises water.

The molar ratio of the water in the extraction agent to the ethanol inthe feed to the second column is preferably at least 0.5:1, e.g., atleast 1:1 or at least 3:1. In terms of ranges, preferred molar ratiosmay range from 0.5:1 to 8:1, e.g., from 1:1 to 7:1 or from 2:1 to 6.5:1.Higher molar ratios may be used but with diminishing returns in terms ofthe additional ethyl acetate in the second distillate and decreasedethanol concentrations in the second column distillate.

In one embodiment, an additional extraction agent, such as water from anexternal source, dimethylsulfoxide, glycerine, diethylene glycol,1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol;ethylene glycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane and chlorinatedparaffins, may be added to second column 123. Some suitable extractionagents include those described in U.S. Pat. Nos. 4,379,028, 4,569,726,5,993,610 and 6,375,807, the entire contents and disclosure of which arehereby incorporated by reference. The additional extraction agent may becombined with the recycled third residue in line 124 and co-fed to thesecond column 123. The additional extraction agent may also be addedseparately to the second column 123. In one aspect, the extraction agentcomprises an extraction agent, e.g., water, derived from an externalsource via line 125 and none of the extraction agent is derived from thethird residue.

Second column 123 may be a tray or packed column. In one embodiment,second column 123 is a tray column having from 5 to 120 trays, e.g.,from 15 to 80 trays or from 20 to 70 trays. The temperature of secondcolumn 123 at atmospheric pressure may vary. Second column 123 mayoperate at a pressure ranging from 0.1 kPa to 510 kPa, e.g., from 1 kPato 475 kPa or from 1 kPa to 375 kPa. In one embodiment second residueexiting in line 126 preferably is at a temperature from 60° C. to 90°C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C. The temperatureof the second distillate exiting in line 127 from second column 123preferably is from 50° C. to 90° C., e.g., from 60° C. to 80° C. or from60° C. to 70° C.

The second residue in line 126 comprises ethanol and water. The secondresidue may comprise less than 3 wt. % ethyl acetate, e.g., less than 1wt. % ethyl acetate or less than 0.5 wt. % ethyl acetate. The seconddistillate in line 127 comprises ethyl acetate, acetaldehyde, and/ordiethyl acetal. In addition, minor amounts of ethanol may be present inthe second distillate. The weight ratio of ethanol in the second residueto second distillate preferably is at least 3:1, e.g., at least 6:1, atleast 8:1, at least 10:1 or at least 15:1.

All or a portion of the third residue is recycled to the second column.In one embodiment, all of the third residue may be recycled untilprocess 100 reaches a steady state at which point a portion of the thirdresidue may be recycled with the remaining portion being purged from thesystem 100. The composition of the second residue will tend to havelower amounts of ethanol than when the third residue is not recycled. Asthe third residue is recycled, the composition of the second residuecomprises less than 30 wt. % of ethanol, e.g., less than 20 wt. % orless than 15 wt. %. The majority of the second residue preferablycomprises water. Notwithstanding this effect, the extractivedistillation step advantageously also reduces the amount of ethylacetate that is sent to the third column, which is highly beneficial inultimately forming a highly pure ethanol product.

As shown, the second residue from second column 123, which comprisesethanol and water, is fed via line 126 to third column 128, alsoreferred to as the “product column.” More preferably, the second residuein line 126 is introduced in the lower part of third column 128, e.g.,lower half or lower third. Third column 128 recovers ethanol, whichpreferably is substantially pure with respect to organic impurities andother than the azeotropic water content, as the distillate in line 129.The distillate of third column 128 preferably is refluxed as shown inFIG. 3, for example, at a reflux ratio of from 1:10 to 10:1, e.g., from1:3 to 3:1 or from 1:2 to 2:1. The third residue in line 124, whichcomprises primarily water, preferably is returned to the second column123 as an extraction agent as described above. In one embodiment, afirst portion of the third residue in line 124 is recycled to the secondcolumn and a second portion is purged and removed from the system vialine 130. In one embodiment, once the process reaches steady state, thesecond portion of water to be purged is substantially similar to theamount of water formed in the hydrogenation of acetic acid. In oneembodiment, a portion of the third residue may be used to hydrolyze anyother stream, such as one or more streams comprising ethyl acetate. Inone embodiment, the third residue in line 124 is withdrawn from thirdcolumn 128 at a temperature higher than the operating temperature of thesecond column 123. Preferably, the third residue in line 124 isintegrated to heat one or more other streams or is reboiled prior to bereturned to the second column 123.

Although FIG. 3 show the third residue being directly recycled to secondcolumn 123, third residue may also be returned indirectly, for example,by storing a portion or all of the third residue in a tank (not shown)or treating the third residue to further separate any minor componentssuch as aldehydes, higher molecular weight alcohols, or esters in one ormore additional columns (not shown).

Third column 128 is preferably a tray column. In one embodiment, thirdcolumn 128 may operate at a pressure from 0.1 kPa to 510 kPa, e.g., from1 kPa to 475 kPa or from 1 kPa to 375 kPa. At atmospheric pressure, thetemperature of the third distillate exiting in line 129 preferably isfrom 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to95° C. The temperature of the third residue in line 124 preferably isfrom 70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to105° C.

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.1 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns in the system 100. Preferably atleast one side stream is used to remove impurities from the third column128. The impurities may be purged and/or retained within the system 100.The composition of the ethanol product obtained from the thirddistillate in FIG. 3 is shown below in Table 5.

The third distillate in line 129 may be further purified to form ananhydrous ethanol product stream, i.e., “finished anhydrous ethanol,”using one or more additional separation systems, such as, for example,distillation columns, adsorption units, membranes, or molecular sieves.Suitable adsorption units include pressure swing adsorption units andthermal swing adsorption unit.

Returning to second column 123, the second distillate preferably isrefluxed as shown in FIG. 3, at a reflux ratio of 1:10 to 10:1, e.g.,from 1:5 to 5:1 or from 1:3 to 3:1. The second distillate in line 127may be purged or recycled to the reaction zone. The second distillate inline 127 may be further processed in an optional fourth column 131, alsoreferred to as the “acetaldehyde removal column.” In optional fourthcolumn 131, the second distillate is separated into a fourth distillate,which comprises acetaldehyde, in line 132 and a fourth residue, whichcomprises ethyl acetate, in line 133. The fourth distillate preferablyis refluxed at a reflux ratio of from 1:20 to 20:1, e.g., from 1:15 to15:1 or from 1:10 to 10:1, and a portion of the fourth distillate isreturned to the reaction zone 101. For example, the fourth distillatemay be combined with the acetic acid feed, added to the vaporizer 106,or added directly to the reactor 103. The fourth distillate preferablyis co-fed with the acetic acid in feed line 105 to vaporizer 106.Without being bound by theory, since acetaldehyde may be hydrogenated toform ethanol, the recycling of a stream that contains acetaldehyde tothe reaction zone increases the yield of ethanol and decreases byproductand waste generation. In another embodiment, the acetaldehyde may becollected and utilized, with or without further purification, to makeuseful products including but not limited to n-butanol, 1,3-butanediol,and/or crotonaldehyde and derivatives.

The fourth residue of optional fourth column 131 may be purged via line133. The fourth residue primarily comprises ethyl acetate and ethanol,which may be suitable for use as a solvent mixture or in the productionof esters. In one preferred embodiment, the acetaldehyde is removed fromthe second distillate in fourth column 131 such that no detectableamount of acetaldehyde is present in the residue of column 131.

Optional fourth column 131 is preferably a tray column as describedabove and preferably operates above atmospheric pressure. In oneembodiment, the pressure is from 120 kPa to 5,000 kPa, e.g., from 200kPa to 4,500 kPa, or from 400 kPa to 3,000 kPa. In a preferredembodiment the fourth column 131 may operate at a pressure that ishigher than the pressure of the other columns.

The temperature of the fourth distillate exiting in line 132 preferablyis from 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C.to 95° C. The temperature of the residue in line 133 preferably is from70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 110°C.

In one embodiment, a portion of the third residue in line 124 isrecycled to second column 123. In one embodiment, recycling the thirdresidue further reduces the aldehyde components in the second residueand concentrates these aldehyde components in second distillate in line127 and thereby sent to the fourth column 131, wherein the aldehydes maybe more easily separated. The third distillate, e.g. intermediatestream, in line 129 may have lower concentrations of aldehydes andesters due to the recycling of third residue in line 124.

Although the composition of the third residue may vary depending on thespecific separation conditions, in preferred embodiments the thirdresidue comprises water and may be referred to herein as a water stream.Due to the presence of acetic acid in the water stream the pH may rangefrom 2.99 to 3.35. In one embodiment, the water stream may besubstantially free of organic impurities, except for acetic acid.Exemplary compositions for the third distillate and third residue (waterstream) are provided below in Table 5. It should also be understood thatthe distillate may also contain other components, not listed, such ascomponents in the feed.

TABLE 5 THIRD COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 75 to 96 80 to 96 85 to 96 Water <12  1 to 9 3 to 8Acetic Acid <1   0.001 to 0.1  0.005 to 0.01  Ethyl Acetate <5   0.001to 4    0.01 to 3   Residue (Water Stream) Water  97 to 100  98 to 100 99 to 100 Ethanol  <0.005 <0.002  <0.001 Ethyl Acetate  <0.001  <0.0005not detectable Acetic Acid <0.5 <0.1  <0.05 Organic Impurities  <0.001 <0.0005 not detectable

As shown in FIG. 3, all or a portion of the third residue stream isdirected to the carbonylation system, e.g., as shown in FIG. 2, to serveas an extraction medium. In a preferred embodiment, all or a portion ofthe third residue is directed to the PRS of the carbonylation system toserve as an extractant (e.g., stream 70 in FIG. 2) for extractingacetaldehyde from a mixture comprising methyl iodide and acetaldehyde.

FIG. 4 illustrates another exemplary separation system that has asimilar reaction zone 101 as FIG. 3 and produces a liquid stream 112,e.g., crude ethanol mixture, for further separation. In one preferredembodiment, the reaction zone 101 of FIG. 4 operates at above 70% aceticacid conversion, e.g., above 85% conversion or above 90% conversion.Thus, the acetic acid concentration in the liquid stream 112 may be low.

Liquid stream 112 is fed to the first column 134 to yield a firstdistillate 135 and first residue 136. Liquid stream 112 may beintroduced in the middle or lower portion of first column 134, alsoreferred to as acid-water column. In one embodiment, no entrainers areadded to first column 134. Water and acetic acid, along with any otherheavy components, if present, are removed from liquid stream 112 and arewithdrawn, preferably continuously, as a first residue in line 136.Preferably, a substantial portion of the water in the crude ethanolmixture that is fed to first column 134 may be removed in the firstresidue, for example, up to about 75% or to about 90% of the water fromthe crude ethanol mixture. In one embodiment, 30 to 90% of the water inthe crude ethanol mixture is removed in the residue, e.g., from 40 to88% of the water or from 50 to 84% of the water.

When first column 134 is operated under about 170 kPa, the temperatureof the residue exiting in line 136 preferably is from 90° C. to 130° C.,e.g., from 95° C. to 120° C. or from 100° C. to 115° C. The temperatureof the distillate exiting in line 135 preferably is from 60° C. to 90°C., e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 134 may also range from 0.1kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 135 comprises some water in addition toethanol and other organics. In terms of ranges, the water concentrationin the first distillate in line 135 preferably is from 4 wt. % to 38 wt.%, e.g., from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. A portion offirst distillate in line 137 may be condensed and refluxed, for example,at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to2:1. It is understood that reflux ratios may vary with the number ofstages, feed locations, column efficiency and/or feed composition.Operating with a reflux ratio of greater than 3:1 may be less preferredbecause more energy may be required to operate the first column 134. Thecondensed portion of the first distillate may also be fed to a secondcolumn 138.

As shown, the remaining portion of the first distillate in line 139 isfed to a water separation unit 140. Water separation unit 140 may be anadsorption unit, membrane, molecular sieves, extractive columndistillation, or a combination thereof. A membrane or an array ofmembranes may also be employed to separate water from the distillate.The membrane or array of membranes may be selected from any suitablemembrane that is capable of removing a permeate water stream from astream that also comprises ethanol and ethyl acetate.

In a preferred embodiment, water separator 140 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure of from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. ThePSA unit may comprise from two to five beds. Water separator 140 mayremove at least 95% of the water from the portion of first distillate inline 139, and more preferably from 99% to 99.99% of the water from thefirst distillate, in a water stream 141. All or a portion of waterstream 141 may be returned to first column 134 in line 142, where thewater preferably is ultimately recovered from column 134 in the firstresidue in line 136. Additionally or alternatively, all or a portion ofwater stream 141 may be removed from the hydrogenation system via line143. The remaining portion of first distillate exits the water separator140 as ethanol mixture stream 144. Ethanol mixture stream 144 may have alow water concentration of less than 10 wt. %, e.g., less than 6 wt. %or less than 2 wt. %.

In this aspect of the invention, either or both the first residue inline 136 and/or the separated stream in line 143 comprise water and maybe referred to as a water stream. Exemplary compositions for line 136and line 143 are provided in Table 6, below. It should also beunderstood that these streams may also contain other components, notlisted, such as components derived from the feed.

TABLE 6 WATER STREAMS IN FIG. 4 Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) First Residue 136 Acetic Acid <90  1 to 50  2 to 35 Water 30 to 10045 to 95 60 to 90 Ethanol <1  <0.9 <0.3 Water Stream 143 Water 80 to 100  85 to 99.5 90 to 99 Ethanol <10 0.001 to 5    0.01 to 0.5  EthylAcetate <10 0.001 to 5    0.01 to 0.5 

In one embodiment, all or a portion of either or both the first residuein line 136 and/or the separated stream in line 143 may be directed tothe carbonylation system, e.g., as shown in FIG. 2, to serve as anextraction medium. In a preferred embodiment, all or a portion of thefirst residue and/or line 143 is directed to the PRS of thecarbonylation system to serve as an extractant (e.g., stream 70 in FIG.2) for extracting acetaldehyde from a mixture comprising methyl iodideand acetaldehyde.

Preferably, ethanol mixture stream 144 is not returned or refluxed tofirst column 135. The condensed portion of the first distillate in line137 may be combined with ethanol mixture stream 144 to control the waterconcentration fed to the second column 138. For example, in someembodiments the first distillate may be split into equal portions, whilein other embodiments, all of the first distillate may be condensed orall of the first distillate may be processed in the water separationunit. In FIG. 4, the condensed portion in line 137 and ethanol mixturestream 144 are co-fed to second column 138. In other embodiments, thecondensed portion in line 137 and ethanol mixture stream 144 may beseparately fed to second column 138. The combined distillate and ethanolmixture has a total water concentration of greater than 0.5 wt. %, e.g.,greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, thetotal water concentration of the combined distillate and ethanol mixturemay be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10wt. %.

The second column 138 in FIG. 4, also referred to as the “light endscolumn,” removes ethyl acetate and acetaldehyde from the firstdistillate in line 137 and/or ethanol mixture stream 144. Ethyl acetateand acetaldehyde are removed as a second distillate in line 145 andethanol is removed as the second residue in line 146. Preferably ethanolis recovered with low amounts of ethyl acetate, acetaldehyde, and/oracetal, e.g., less than 1 wt. % or more preferably less than 0.5 wt. %.The ethanol product obtained from second residue in FIG. 4, is shownbelow in Table 8. Preferably, the ethanol product comprises less than 1wt. % diethyl acetal, e.g., less than 0.5 wt. % or less than 0.01 wt. %.

Second column 138 may be a tray column or packed column. In oneembodiment, second column 138 is a tray column having from 5 to 120trays, e.g., from 15 to 100 trays or from 20 to 90 trays. In oneembodiment, second column 138 operates at a pressure from 101 kPa to5,000 kPa, e.g., from 120 kPa to 4,000 kPa, or from 150 kPa to 3,000kPa. In other embodiments, second column 138 may operate at a pressureranging from 0.1 kPa to 510 kPa, e.g., from 10 kPa to 450 kPa or from 50kPa to 350 kPa. Although the temperature of second column 138 may vary,when at about 20 kPa to 70 kPa, the temperature of the second residueexiting in line 146 preferably is from 30° C. to 75° C., e.g., from 35°C. to 70° C. or from 40° C. to 65° C. The temperature of the seconddistillate exiting in line 145 preferably is from 20° C. to 55° C.,e.g., from 25° C. to 50° C. or from 30° C. to 45° C.

The total concentration of water fed to second column 138 preferably isless than 10 wt. %, as discussed above. When first distillate in line137 and/or ethanol mixture stream 144 comprises minor amounts of water,e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may befed to the second column 138 as an extractive agent in the upper portionof the column. A sufficient amount of water is preferably added via theextractive agent such that the total concentration of water fed tosecond column 138 is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %,based on the total weight of all components fed to second column 138. Ifthe extractive agent comprises water, the water may be obtained from anexternal source or from an internal return/recycle line from one or moreof the other columns or water separators.

Suitable extractive agents may also include, for example,dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane, chlorinatedparaffins, or a combination thereof. When extractive agents are used, asuitable recovery system, such as a further distillation column, may beused to recycle the extractive agent.

The second distillate in line 145, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 4, for example, ata reflux ratio of from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3to 3:1. In one aspect, not shown, the second distillate 145 or a portionthereof may be returned to reactor 103.

In one embodiment, the second distillate in line 145 and/or a refinedsecond distillate, or a portion of either or both streams, may befurther separated to produce an acetaldehyde-containing stream and anethyl acetate-containing stream. For example, the optional fourth column131 of FIG. 3 may be used to separate second distillate in line 145.This may allow a portion of either the resulting acetaldehyde-containingstream or ethyl acetate-containing stream to be recycled to reactor 103while purging the other stream. The purge stream may be valuable as asource of either ethyl acetate and/or acetaldehyde. In one embodiment,it may be preferred to operate second column 138 in FIG. 4 at a pressureless than atmospheric pressure to decrease the energy required toseparate ethyl acetate and ethanol.

Another exemplary two column separation scheme is shown in FIG. 5. Inthis embodiment, liquid stream 112 is introduced in the upper part offirst column 160, e.g., upper half or upper third. In one embodiment, noentrainers are added to first column 160. In first column 160, a weightmajority of the ethanol, water, acetic acid, and other heavy components,if present, are removed from liquid stream 112 and are withdrawn,preferably continuously, as the first residue in line 162. First column160 also forms an overhead distillate, which is withdrawn in line 161,and which may be condensed and refluxed, for example, at a ratio of from30:1 to 1:30, e.g., from 10:1 to 1:10 or from 1:5 to 5:1. The firstdistillate in line 161 preferably comprises a weight majority of theethyl acetate from liquid line 112. In addition, distillate in line 161may also comprise acetaldehyde.

When column 160 is operated under about 170 kPa, the temperature of theresidue exiting in line 162 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The base of column 160may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, water, and acetic acid, therebyproviding an energy efficiency advantage. The temperature, at 170 kPa,of the distillate exiting in line 161 preferably is from 75° C. to 100°C., e.g., from 75° C. to 83° C. or from 81° C. to 84° C.

In one embodiment, column 160 of FIG. 5 may be operated at a temperaturewhere most of the water, ethanol, and acetic acid are removed from theresidue stream and only a small amount of ethanol and water is collectedin the distillate stream due to the formation of binary and tertiaryazeotropes. The weight ratio of water in the residue in line 162 towater in the distillate in line 161 may be greater than 1:1, e.g.,greater than 2:1. The weight ratio of ethanol in the residue to ethanolin the distillate may be greater than 1:1, e.g., greater than 2:1.

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in reactor 103. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g.,comprising less than 1000 ppm, less than 500 ppm or less than 100 ppmacetic acid. The distillate may be purged from the system or recycled inwhole or part to reactor 103. In some embodiments, the distillate may befurther separated, e.g., in an optional fourth column of FIG. 3, into anacetaldehyde stream and an ethyl acetate stream. Either of these streamsmay be returned to the reactor 103 or separated from system 100 as aseparate product.

To recover ethanol, the residue in line 162 may be further separated ina second column 163, also referred to as an “acid separation column.” Anacid separation column may be used when the acetic acid concentration inthe first residue is greater than 1 wt. %, e.g., greater than 5 wt. %.The first residue in line 162 is introduced to second column 163preferably in the top part of column 163, e.g., top half or top third.Second column 163 yields a second residue in line 165 comprising aceticacid and water, and a second distillate in line 164 comprising ethanol.

Second column 163 may be a tray column or packed column. In oneembodiment, second column 163 is a tray column having from 5 to 150trays, e.g., from 15 to 50 trays or from 20 to 45 trays. In someembodiments, the second column 163 of FIG. 5 is operated at a pressureranging from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1kPa to 375 kPa. In the system shown in FIG. 5, it is preferred tooperate the first column 160 at an increased pressure, because secondcolumn 163 comprises very low amounts of acetaldehyde and/or acetals. Atatmospheric pressure the temperature of the second residue exiting inline 165 preferably is from 95° C. to 130° C., e.g., from 100° C. to125° C. or from 110° C. to 120° C. The temperature of the seconddistillate exiting in line 164 preferably is from 60° C. to 105° C.,e.g., from 75° C. to 100° C. or from 80° C. to 100° C.

The weight ratio of ethanol in the second distillate in line 164 toethanol in the second residue in line 165 preferably is at least 35:1.In one embodiment, the weight ratio of water in the second residue 165to water in the second distillate 164 is greater than 2:1, e.g., greaterthan 4:1 or greater than 6:1. In addition, the weight ratio of aceticacid in the second residue 165 to acetic acid in the second distillate164 preferably is greater than 10:1, e.g., greater than 15:1 or greaterthan 20:1. Preferably, the second distillate in line 164 issubstantially free of acetic acid and may only contain, if any, traceamounts of acetic acid. Preferably, the second distillate in line 164contains substantially no ethyl acetate.

The remaining water from the second distillate in line 164 may beremoved in further embodiments of the present invention. Depending onthe water concentration, the ethanol product may be derived from thesecond distillate in line 164. Some applications, such as industrialethanol applications, may tolerate water in the ethanol product, whileother applications, such as fuel applications, may require an anhydrousethanol. The amount of water in the distillate of line 164 may be closerto the azeotropic amount of water, e.g., at least 4 wt. %, preferablyless than 20 wt. %, e.g., less than 12 wt. % or less than 7.5 wt. %.Water may be removed from the second distillate in line 164 usingseveral different separation techniques as described herein.Particularly preferred techniques include the use of distillationcolumn, membranes, adsorption units, and combinations thereof.

In one embodiment of the invention, the second residue 165 comprisesprimarily water and may be referred to as a water stream. Exemplarycompositions for second residue 165 are provided in Table 7, below.

TABLE 7 EXEMPLARY COMPOSITIONS FOR WATER STREAM 165 IN FIG. 5 Conc. (wt.%) Conc. (wt. %) Conc. (wt. %) Acetic Acid 0.1 to 45  0.2 to 40  0.5 to35  Water  45 to 100   55 to 99.8   65 to 99.5 Ethyl Acetate <2 <1  <0.5Ethanol <5 0.001 to 5    <2

In one embodiment, all or a portion of the second residue 165 isdirected to a carbonylation system, e.g., as shown in FIG. 2, to serveas an extraction medium. In a preferred embodiment, all or a portion ofthe second residue 165 is directed to the PRS of the carbonylationsystem to serve as an extractant (e.g., stream 70 in FIG. 2) forextracting acetaldehyde from a mixture comprising methyl iodide andacetaldehyde.

In one embodiment, any of the residue streams from FIGS. 3-5 may beseparated into an acetic acid stream and a water stream when the residuecomprises a majority of acetic acid, e.g., greater than 50 wt. %. Aceticacid may also be recovered in some embodiments from the residue having alower acetic acid concentration. The residue may be separated into theacetic acid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to the reactor 103. The resultingwater stream may be directed to a carbonylation system for use as anextractant as discussed above.

In other embodiments, for example, where the second residue comprisesless than 50 wt. % acetic acid, possible options include one or more of:(i) neutralizing the acetic acid, or (ii) reacting the acetic acid withan alcohol. It also may be possible to separate a residue comprisingless than 50 wt. % acetic acid using a weak acid recovery distillationcolumn to which a solvent (optionally acting as an azeotroping agent)may be added. Exemplary solvents that may be suitable for this purposeinclude ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate,vinyl acetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue comprises less than 10 wt. %acetic acid. Acetic acid may be neutralized with any suitable alkali oralkaline earth metal base, such as sodium hydroxide or potassiumhydroxide. When reacting acetic acid with an alcohol, it is preferredthat the residue comprises less than 50 wt. % acetic acid. The alcoholmay be any suitable alcohol, such as methanol, ethanol, propanol,butanol, or mixtures thereof. The reaction forms an ester that may beintegrated with other systems, such as carbonylation production or anester production process. Preferably, the alcohol comprises ethanol andthe resulting ester comprises ethyl acetate. Optionally, the resultingester may be fed to the hydrogenation reactor.

The columns shown in figures may comprise any distillation columncapable of performing the desired separation and/or purification. Forexample, other than the acid columns describe above, the other columnspreferably are a tray column having from 1 to 150 trays, e.g., from 10to 100 trays, from 20 to 95 trays or from 30 to 75 trays. The trays maybe sieve trays, fixed valve trays, movable valve trays, or any othersuitable design known in the art. In other embodiments, a packed columnmay be used. For packed columns, structured packing or random packingmay be employed. The trays or packing may be arranged in one continuouscolumn or they may be arranged in two or more columns such that thevapor from the first section enters the second section while the liquidfrom the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. As will be recognized by thoseskilled in the art, the temperature at a given location in an operatingdistillation column is dependent on the composition of the material atthat location and the pressure of column. In addition, feed rates mayvary depending on the size of the production process and, if described,may be generically referred to in terms of feed weight ratios.

The final ethanol product produced by the processes of the presentinvention may be taken from a stream that primarily comprises ethanolfrom exemplary systems shown in the figures. The ethanol product may bean industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the ethanol product. Exemplary finished ethanolcompositional ranges are provided below in Table 8.

TABLE 8 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 99.9   80 to 99.5 85 to 96 Water <12  1to 9 3 to 8 Acetic Acid <1   <0.1 <0.01 Ethyl Acetate <2   <0.5 <0.05Diethyl Acetal <1   0.0001 to 0.1   0.0001 to 0.01  Acetone  <0.05 <0.01  <0.005 Isopropanol <0.5 <0.1 <0.05 n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be greater than indicated in Table 8, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingfuels, solvents, chemical feedstocks, pharmaceutical products,cleansers, sanitizers, hydrogenation transport or consumption. In fuelapplications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, ethyl benzene, aldehydes,butadiene, and higher alcohols, especially butanol. In the production ofethyl acetate, the finished ethanol composition may be esterified withacetic acid. In another application, the finished ethanol compositionmay be dehydrated to produce ethylene. Any known dehydration catalystcan be employed to dehydrate ethanol, such as those described incopending U.S. Pub. Nos. 2010/0030002 and 2010/0030001, the entirecontents and disclosures of which are hereby incorporated by reference.A zeolite catalyst, for example, may be employed as the dehydrationcatalyst. Preferably, the zeolite has a pore diameter of at least about0.6 nm, and preferred zeolites include dehydration catalysts selectedfrom the group consisting of mordenites, ZSM-5, a zeolite X and azeolite Y. Zeolite X is described, for example, in U.S. Pat. No.2,882,244 and zeolite Y in U.S. Pat. No. 3,130,007, the entireties ofwhich are hereby incorporated herein by reference.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited above and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with other embodiments as willbe appreciated by one of skill in the art. Furthermore, those ofordinary skill in the art will appreciate that the foregoing descriptionis by way of example only, and is not intended to limit the invention.

We claim:
 1. A process for producing ethanol, the process comprising thesteps of: carbonylating methanol in a carbonylation system in thepresence of a carbonylation catalyst under conditions effective to formacetic acid; hydrogenating the acetic acid in a hydrogenation system inthe presence of a hydrogenation catalyst to form a crude ethanol productcomprising ethanol and water; separating the ethanol from the water toform an ethanol stream and a water stream; and directing at least aportion of the water stream to the carbonylation system.
 2. The processof claim 1, wherein the water stream is used as an extractant in thecarbonylation system.
 3. The process of claim 1, wherein thecarbonylation process forms a PRC stream comprising one or more PRC'sand methyl iodide, the process further comprising the step of: adding atleast a portion of the water stream to the PRC stream to form an aqueousphase comprising the separated water and a majority of the one or morePRC's, and an organic phase comprising a majority of the methyl iodide.4. The process of claim 1, wherein the water stream is essentially freeof organic impurities other than acetic acid.
 5. The process of claim 1,wherein the crude ethanol product comprises ethanol, water, and ethylacetate.
 6. The process of claim 5, wherein the crude ethanol productcomprises ethanol in an amount of from 5 to 70 wt. %, water in an amountof from 5 to 35 wt. %, and ethyl acetate in an amount of from 0 to 20wt. %.
 7. The process of claim 1, wherein the water stream comprises: atleast 97 wt. % water; less than 0.5 wt. % acetic acid; less than 0.005wt. % ethanol; and less than 0.001 wt. % ethyl acetate.
 8. The processof claim 1, wherein the water stream has a pH ranging from 2.99 to 3.35.9. The process of claim 1, wherein the separating comprises: separatingat least a portion of the crude ethanol product in a first column into afirst distillate comprising ethanol, water and ethyl acetate, and afirst residue comprising water; separating at least a portion of thefirst distillate in a second column into a second distillate comprisingethyl acetate and a second residue comprising ethanol and water; andseparating at least a portion of the second residue in a third columninto a third distillate comprising ethanol and a third residuecomprising the water stream.
 10. The process of claim 9, wherein thesecond column is an extractive distillation column, which utilizes anextraction agent.
 11. The process of claim 10, wherein at least aportion of the water stream is directed to the second column.
 12. Theprocess of claim 1, wherein the hydrogenation catalyst comprises acombination of metals selected from the group consisting ofplatinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, platinum/tin, cobalt/palladium, cobalt/platinum,cobalt/chromium, cobalt/ruthenium, silver/palladium, copper/palladium,nickel/palladium, gold/palladium, ruthenium/rhenium, and ruthenium/iron.13. The process of claim 1, wherein the separating comprises: separatingat least a portion of the crude ethanol product in a first column into afirst distillate comprising ethyl acetate, acetaldehyde and ethanol, anda first residue comprising water and acetic acid, wherein the waterstream that is directed to the carbonylation system is an aliquot ornon-aliquot portion of the first residue.
 14. The process of claim 1,wherein the separating comprises: separating at least a portion of thecrude ethanol product in a first column into a first distillatecomprising ethyl acetate, acetaldehyde and ethanol, and a first residuecomprising water and acetic acid, wherein at least a portion of thewater stream that is directed to the carbonylation system is derivedfrom the first residue.
 15. The process of claim 14, wherein the firstdistillate further comprises water and the process further comprises thestep of removing additional water from the first distillate, wherein atleast a portion of the water stream that is directed to thecarbonylation system is derived from the additional water.
 16. A processfor producing a water stream, the process comprising: providing a crudeethanol product comprising ethanol, water, ethyl acetate, and aceticacid; separating at least a portion of the crude ethanol product into anethanol stream and a water stream, wherein the water stream isessentially free of organic impurities other than acetic acid; anddirecting at least a portion of the water stream to a carbonylationsystem.
 17. The process of claim 16, wherein the water stream is used asan extractant in the carbonylation system.
 18. The process of claim 16,wherein the carbonylation process forms a PRC stream comprising one ormore PRC's and methyl iodide, the process further comprising the stepof: adding at least a portion of the water stream to the PRC stream toform an aqueous phase comprising the separated water and a majority ofthe one or more PRC's, and an organic phase comprising a majority of themethyl iodide.
 19. The process of claim 16, wherein the water stream isessentially free of organic impurities other than acetic acid.